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This was tested on Ubuntu 12.04 (Precise) LTS Server. It returns the name of the symlink within /dev/disk/by-id for the physical drive you specify. Change /dev/sda to the one you want, and replace ata- with scsi- or the appropriate type for your drive.

I used this to pre-configure grub-pc during a non-interactive install because I had to tell it which disk to install grub on, and physical disks don't have a UUID such as that blkid provides.

"That's it. Not much to see here. The first command writes any cache data that hasn't been written to the disk out to the disk. The second command tells the kernel to drop what's cached. Not much to it. This invalidates the write cache as well as the read cache, which is why we have the sync command first. Supposedly, it is possible to have some cached write data never make it to disk, so use it with caution, and NEVER do it on a production server. You could ... but why take the risk?

This is a little trickier than finding the last Sunday, because you know the last Sunday is in the first position of the last line. The trick is to use the NF less than or equal to 7 so it picks up all the lines then grep out any empty lines.